fix: Incorrect scroll percentage calculation in scrollHorizontal method

Change scroll percentage calculation approach. Use getScrollWidth instead of getCanvasWidth as a denominator.
Add width of scroll to scroll length for percentage not to exceed 1.

Author: vkorolev

src/js/core/factories/GridRenderContainer.js

@@ -303,6 +303,10 @@ angular.module('ui.grid')
     return this.getCanvasHeight() - this.getViewportHeight() + this.grid.scrollbarHeight;
   };
 
+  GridRenderContainer.prototype.getHorizontalScrollLength = function getHorizontalScrollLength() {
+    return this.getCanvasWidth() - this.getViewportWidth() + this.grid.scrollbarWidth;
+  };
+
   GridRenderContainer.prototype.getCanvasWidth = function getCanvasWidth() {
     var self = this;
 
@@ -375,7 +379,7 @@ angular.module('ui.grid')
       if (xDiff > 0) { this.grid.scrollDirection = uiGridConstants.scrollDirection.RIGHT; }
       if (xDiff < 0) { this.grid.scrollDirection = uiGridConstants.scrollDirection.LEFT; }
 
-      var horizScrollLength = (this.canvasWidth - this.getViewportWidth());
+      var horizScrollLength = this.getHorizontalScrollLength();
       if (horizScrollLength !== 0) {
         horizScrollPercentage = newScrollLeft / horizScrollLength;
       }
@@ -487,8 +491,7 @@ angular.module('ui.grid')
 
     // Calculate the scroll percentage according to the scrollLeft location, if no percentage was provided
     if ((typeof(scrollPercentage) === 'undefined' || scrollPercentage === null) && scrollLeft) {
-      var horizScrollLength = (self.getCanvasWidth() - self.getViewportWidth());
-      scrollPercentage = scrollLeft / horizScrollLength;
+      scrollPercentage = scrollLeft / self.getHorizontalScrollLength();
     }
 
     var colIndex = Math.ceil(Math.min(maxColumnIndex, maxColumnIndex * scrollPercentage));